East Marginal Way S Preservation (FHWA)

This memorandum provides geotechnical analysis and foundation design recommendations for four new traffic signal poles at the East Marginal Way South and Corson Avenue South intersection in Seattle, WA. The scope includes a review of existing geotechnical data, identification of site features (soil zones, contamination, groundwater), classification of the subsurface as “Lower Strength Soil,” and detailed construction considerations for drilled‑shaft foundations, including utility locate procedures, casing, concrete placement, and potential obstructions. The client (SDOT) will use these recommendations to develop design specifications and construction documents for the signal‑pole project, which is part of a larger pavement overlay and bike‑lane improvement effort. • Review of existing geotechnical information and mapping of site features. • Soil strength classification and recommendation of “Lower Strength Soil” design zone. • Construction guidance for drilled‑shaft foundations (casing, slurry, concrete placement, obstruction handling). • Utility locate recommendations and back‑fill procedures. • Limitations of the study and optional follow‑on services (RFI review, submittal review, construction support).